Ultralong Organic Phosphorescence: From Material Design to Applications

Modulating room temperature phosphorescence of acrylamide by stepwise rigidification for its detection in potato crisps

The selective detection of acrylamide (AA) is crucial, which is limited by the high background and interferences from food matrix. A room temperature phosphorescence (RTP) assay was developed through modulating its RTP by a stepwise rigidification strategy. The first step rigidification resulted in crosslinking of AA and denser of hydrogen bonding. This prompted the RTP efficiency from <0.1 to 3.8 % and emission lifetime of AA (from 3.0 μs to 0.29 s). Introducing boric acid resulted in the second step rigidification, triggered the formation of rigid matrix and chemical bonding. These synergistic effects prompted the photoluminescence quantum yield to 23.7 % and emission lifetime to 1.20 s. AA was quantitatively detected through monitoring the RTP intensity, with a limit of detection of 0.9 μg/mL. Benefiting from the delayed signal detection, background signal and the interferences from food matrices were eliminated, endowing the detection of AA in practical food samples.

Fluorescent zinc(II) thione and selone complexes for light-emitting applications

Three 1-(anthracene-9-ylmethyl)-3-isopropyl-imidazol-2-thione Zn(II) halide complexes (1-3) and one 1-(anthracene-9-ylmethyl)-3-isopropyl-imidazol-2-selone Zn(II) dichloride complex (4) were synthesized and characterized. Complexes 2, 3, and 4 exhibited distorted tetrahedral geometries, while complex 1 adopted a regular tetrahedral geometry. All these complexes displayed emission in the crystalline state, with complex 3 emitting in the yellow region and complex 1 and 4 in the blue region, while complex 2 gave a bluish-green emission. The ligands L1 and L2, however, showed no emission in the solution and crystalline state. The photophysical properties of these four complexes were studied, and their quantum yields in the crystalline states were determined. Complex 1 exhibited the highest quantum yield of 7.72%, and complexes 2 and 3 demonstrated 5.95% and 5.07% yield, respectively. Complex 4 exhibited a relatively lower quantum yield of 3.87%. The crystalline state quantum yields for the complexes were found to vary with the variation of the halide ion coordinated to the metal center, following the trend Cl- > Br- > I-. The quantum yield for the thione complexes 1-3 was found to be superior to that of the selone complex 4. Density functional theory calculations were performed to study their structural properties and emissive nature. TD-DFT natural transition orbital calculations revealed that the observed emission behaviour is primarily driven by intra-ligand charge transfer (1ILCT) mediated through the metal center.

Epitaxial Growth of Silver Clusters from Ag57 to Ag72 via Laminating Multiple Different Anion Templates

The established capability of anion templates in precisely manipulating the size, geometry, and function of metal clusters is well acknowledged. However, the development of a systematic methodology for orchestrating the assembly of silver clusters, particularly those encompassing multiple distinct types of anion templates, remains elusive due to the formidable synthetic challenge. In this work, we report two novel silver clusters, Ag57 and Ag72, using two and three different anion templates, respectively. Ag57 features a gyroscope-like monovalent cation with an Ag3 triangle core sandwiched by one [SiW9O34]10- and a triad of Cl- anion templates. By intentionally introducing the third anion template, SO4 2-, the structure is expanded to the unprecedented Ag72 (with 15 silver atoms epitaxially grown on top of Ag57) resembling a tumbler, inside of which two Ag3 layers are laminated by one [SiW9O34]10-, seven Cl- and one SO4 2- anion templates in parallel with respect to longitudinal orientation. It is noteworthy that Ag72 exhibits remarkable structural complexity and represents a pioneering achievement as the first silver cluster incorporating three distinct types of anion templates. In addition, Ag72 demonstrates a significant advantage over Ag57, particular in terms of applications such as luminescent thermometers and remote laser ignition. This work not only broadens the horizon for precise control of the silver cluster structures through the integration of multiple types of hetero-anions but also lays a solid foundation for potential optical applications in the future.

Organic Materials with Ultrabright Phosphorescence at Room Temperature under Physiological Conditions for Bioimaging

In contrast to the high efficiency of room temperature phosphorescence in crystal states, the generally utilized nanoparticles of organic materials in bioimaging demonstrated sharply decreased performance by orders of magnitude under physiological conditions, badly limiting the realization of their unique advantages. This case, especially for organic red/near-infrared (NIR) phosphorescence materials, is not only the challenge present in reality but more importantly, for the theoretical problem of deeply understanding and avoiding the quenching effect by oxygen and water toward excited triplet states. Herein, thanks to the intelligent molecular design by the introduction of abundant hydrophobic chains and highly-branched structures, bright and persistent red/NIR phosphorescence under physiological conditions has been realized, which demonstrated the shielding effect towards oxygen, and the strengthened intermolecular interactions to suppress the non-radiative transitions. Accordingly, the record phosphorescence intensity of nanoparticles in bioimage, up to 8.21±0.36×108 p s-1 cm-2 sr-1, was achieved, to realize the clear phosphorescence imaging of liver and tumors in living mice, even lymph nodes in rabbit models with high SBRs. This work afforded an efficient way to achieve the bright red/NIR phosphorescence nanoparticles, guiding their further applications in biology and medicine.

Hydrogen-Bonded Organic Framework Nanoscintillators for X-Ray-Induced Photodynamic Therapy in Hepatocellular Carcinoma

X-ray induced photodynamic therapy (X-PDT) leverages penetrating X-ray to generate singlet oxygen (1O2) for treating deep-seated tumors. However, conventional X-PDT typically relies on heavy metal inorganic scintillators and organic photosensitizers to produce 1O2, which presents challenges related to toxicity and energy conversion efficiency. In this study, highly biocompatible organic phosphorescent nanoscintillators based on hydrogen-bonded organic frameworks (HOF) are designed and engineered, termed BPT-HOF@PEG, to enhance X-PDT in hepatocellular carcinoma (HCC) treatment. BPT-HOF@PEG functions simultaneously as both scintillator and photosensitizer, effectively absorbing and transferring X-ray energy to generate abundant 1O2. Both in vitro and in vivo investigations demonstrate that internalized BPT-HOF@PEG efficiently produces significant quantities of 1O2 upon X-ray irradiation. Additionally, X-ray exposure directly inflicts DNA damage, and the synergistic effects of these mechanisms result in pronounced cell death and substantial tumor growth inhibition, with a significant inhibition rate of up to 90.4% in vivo assessments. RNA sequencing analyses reveal that X-PDT induces apoptosis in Hepa1-6 cells while inhibiting cell proliferation, culminating in tumor cell death. Therefore, this work highlights the considerable potential of efficient phosphorescent HOF nanoscintillators-based X-PDT as a promising therapeutic approach for HCC, providing a highly effective alternative with negligible toxicity for patients with unresectable tumors.

Activating Ultralong Room-Temperature Phosphorescence of Mono-Ring Arylboronic Acid by Hydrogen Bond for Tunable Afterglow Color and Stimulus Response

Activating the ultralong room-temperature phosphorescence (RTP) of mono-ring arylboronic acid remains a great challenge, because the capacious free spaces shaped by a rubbery polymeric matrix allow the benzene ring skeleton to freely rotate. Herein, the ultralong RTP in mono-ring arylboronic acid derivatives embedded in a polyvinyl alcohol (PVA) matrix is activated, leveraging enhanced intermolecular and intramolecular hydrogen bonding and activating ultralong RTP. By incorporating diverse PBA derivatives into PVA via click chemistry, 3-aminophenylboronic acid (3A-PBA) doped PVA films showcase the most extended RTP lifetimes (2.24 s) and a high quantum yield (11.2%), alongside rapid and sensitive explosive vapor detection capabilities. These findings not only address the activation challenges of RTP in organic systems by highlighting the crucial role of hydrogen bonding and Förster resonance energy transfer in color tunability, but also mark a significant stride toward overcoming the limitations of current luminescent materials. This work heralds a new era in the development of organic phosphorescent materials, offering a promising strategy for broadening their practical applications and enhancing performance, particularly in environmental monitoring and security.

Red Room Temperature Phosphorescence in Non-Aromatic Carbonized Polymer Dots

Achieving red organic room temperature phosphorescence (RTP) remains a significant challenge, especially in a non-aromatic system. Herein, red RTP with emission at 605 and 645 nm is achieved through inducing and confining carboxyl dimer association (CDA), a unique hydrogen-bonded coupling red phosphorescence unit, in non-aromatic carbonized polymer dots (CPDs). The CPDs are synthesized via microwave method by using polyacrylic acid (PAA), succinic acid (SA), and traces of phosphoric acid as precursors. Small molecule SA can flexibly enter the polymer cluster of PAA and pair with the isolated carboxyl groups to form CDA. The intrinsic local carbonized structure formed in CPDs can effectively stabilize CDA to achieve red RTP. The red afterglow can last for 1 s to naked eye, and the corresponding lifetimes for emission at 605 and 645 nm were 61 and 45 ms, respectively, after 365 nm excitation off. This work not only reported the non-aromatic red organic RTP materials for the first time, but also explored CPDs as an effective platform for achieving such non-aromatic long-wavelength RTP.

Facile Synthesis of Ln-Doped Hydrogen-Bonded Organic Frameworks with Rare-Earth-Characteristic Long Persistent Luminescence

Tunable luminescence-assisted information storage and encryption holds increasing significance in today's society. A promising approach to incorporating the benefits of both organic long persistent luminescent (LPL) materials and rare-earth (RE) luminescence lies in utilizing organic host materials to sensitize RE luminescence, as well as employing Förster resonance energy transfer from hydrogen-bonded organic framework (HOF) phosphorescence to RE compound luminescence. This work introduces a one-pot, in situ pyrolytic condensation method, achieved through high-temperature melting calcination, to synthesize lanthanide ion-doped HOF materials. This method circumvents the drawback of molecular triplet energy annihilation, enabling the creation of organic LPL materials with RE characteristics. The HOF material serves as the host, exhibiting blue phosphorescence and cyan LPL. By fine-tuning the doping amount, the composite material U-Tb-100 achieves green LPL with a luminescent quantum yield of 56.4 %, and an LPL duration of approximately 2-3 s, demonstrating tunable persistence. Single-crystal X-ray diffraction, spectral analysis, and theoretical calculation unveil that U-Tb-100 exhibits exceptional quantum yield and long-lived luminescence primarily due to the efficient sensitization of U monomer to RE ions and the PRET process between U and RE complexes. This ingenious strategy not only expands the repertoire of HOF materials but also facilitates the design of multifunctional LPL materials.

High-yield upcycling of feather wastes into solid-state ultra-long phosphorescence carbon dots for advanced anticounterfeiting and information encryption

Recently, biomass-derived carbon dots (CDs) have attracted considerable attention in high-technology fields due to their prominent merits, including brilliant luminescence, superior biocompatibility, and low toxicity. However, most of the biomass-derived CDs only show bright fluorescence in diluted solution because of aggregation-induced quenching effect, hence cannot exhibit solid-state long-lived room-temperature phosphorescence (RTP) in ambient conditions. Herein, matrix-free solid-state RTP with an average lifetime of 0.50 s is realized in the CDs synthesized by one-pot hydrothermal treatment of duck feather waste powder. To further enhance RTP lifetime, hydrogen bonding is introduced by employing polyols like polyvinyl alcohol (PVA) and phytic acid (PA), and a bimodal luminescent CDs/PVA/PA ink is exploited by mixing the CDs and polyols. Astonishingly, the CDs/PVA/PA ink screen-printed onto cellulosic substrates exhibits unprecedented green RTP with average lifetime of up to 1.97 s, and the afterglow lasts for more than 14 s after removing UV lamp. Such improvement on RTP is proposed to the populated excited triplet excitons stabilized by rigid chains. Furthermore, the CDs/PVA/PA ink demonstrates excellent potential in anticounterfeiting and information encryption. To the best of the authors' knowledge, this work is the first successful attempt to fabricate matrix-free ultra-long RTP CDs by reclamation of the feather wastes for environmental sustainability.

Nanomaterials for Flexible Neuromorphics

The quest to imbue machines with intelligence akin to that of humans, through the development of adaptable neuromorphic devices and the creation of artificial neural systems, has long stood as a pivotal goal in both scientific inquiry and industrial advancement. Recent advancements in flexible neuromorphic electronics primarily rely on nanomaterials and polymers owing to their inherent uniformity, superior mechanical and electrical capabilities, and versatile functionalities. However, this field is still in its nascent stage, necessitating continuous efforts in materials innovation and device/system design. Therefore, it is imperative to conduct an extensive and comprehensive analysis to summarize current progress. This review highlights the advancements and applications of flexible neuromorphics, involving inorganic nanomaterials (zero-/one-/two-dimensional, and heterostructure), carbon-based nanomaterials such as carbon nanotubes (CNTs) and graphene, and polymers. Additionally, a comprehensive comparison and summary of the structural compositions, design strategies, key performance, and significant applications of these devices are provided. Furthermore, the challenges and future directions pertaining to materials/devices/systems associated with flexible neuromorphics are also addressed. The aim of this review is to shed light on the rapidly growing field of flexible neuromorphics, attract experts from diverse disciplines (e.g., electronics, materials science, neurobiology), and foster further innovation for its accelerated development.

Light/X-ray/ultrasound activated delayed photon emission of organic molecular probes for optical imaging: mechanisms, design strategies, and biomedical applications

Conventional optical imaging, particularly fluorescence imaging, often encounters significant background noise due to tissue autofluorescence under real-time light excitation. To address this issue, a novel optical imaging strategy that captures optical signals after light excitation has been developed. This approach relies on molecular probes designed to store photoenergy and release it gradually as photons, resulting in delayed photon emission that minimizes background noise during signal acquisition. These molecular probes undergo various photophysical processes to facilitate delayed photon emission, including (1) charge separation and recombination, (2) generation, stabilization, and conversion of the triplet excitons, and (3) generation and decomposition of chemical traps. Another challenge in optical imaging is the limited tissue penetration depth of light, which severely restricts the efficiency of energy delivery, leading to a reduced penetration depth for delayed photon emission. In contrast, X-ray and ultrasound serve as deep-tissue energy sources that facilitate the conversion of high-energy photons or mechanical waves into the potential energy of excitons or the chemical energy of intermediates. This review highlights recent advancements in organic molecular probes designed for delayed photon emission using various energy sources. We discuss distinct mechanisms, and molecular design strategies, and offer insights into the future development of organic molecular probes for enhanced delayed photon emission.

Hydrostatic pressure effect on excited state properties of room temperature phosphorescence molecules: A QM/MM study

Stimulus-responsive organic room temperature phosphorescence (RTP) materials exhibit variations in their luminescent characteristics (lifetime and efficiency) upon exposure to external stimuli, including force, heat, light and acid-base conditions, the development of stimulus-responsive RTP molecules becomes imperative. However, the inner responsive mechanism is unclear, theoretical investigations to reveal the relationship among hydrostatic pressures, molecular structures and photophysical properties are highly desired. Herein, taking the Se-containing RTP molecule (SeAN) as a model, based on the dispersion corrected density functional theory (DFT-D), the combined quantum mechanics and molecular dynamics (QM/MM) method and thermal vibration correlation function (TVCF) theory, the influences of hydrostatic pressure on molecular structures, transition properties as well as lifetimes and efficiencies of RTP molecule are theoretically studied. Results show that extended lifetime and enhanced efficiency are observed at 2 Gpa compared with molecule at normal pressure, and this is related with the small reorganization energy and large oscillator strength. Moreover, due to the small energy gap (0.34 eV) and remarkable spin-orbit coupling (SOC) constant (8.56 cm-1) between first singlet excited state and triplet state, fast intersystem crossing (ISC) process is determined for molecule at 6 Gpa. Furthermore, the intermolecular interactions are visualized using independent gradient model based on Hirshfeld partition (IGMH) and the changes of molecular packing modes, SOC values, lifetimes and efficiencies with pressures are detected. These results reveal the relationship between molecular structures and RTP properties. Our work provides theoretical insights into the hydrostatic pressure response mechanism and could promote the development new efficient stimulus-responsive molecules.

From Simple Probe to Smart Composites: Water-Soluble Pincer Complex With Multi-Stimuli-Responsive Luminescent Behaviors

Water-soluble smart materials with multi-stimuli-responsiveness and ultra-long room-temperature phosphorescence (RTP) have garnered broad attention. Herein, a water-soluble terpyridine zinc complex (MeO-Tpy-Zn-OAc), featuring a simple donor-π-acceptor (D-π-A) structure is presented, which responds to a variety of stimuli, including changes in solvents, pH, temperature, and the addition of amino acids. Notably, MeO-Tpy-Zn-OAc functions as a fluorescence probe, capable of visually and selectively discriminating aspartate or histidine among other common amino acids in water. Additionally, when incorporated into polyvinyl alcohol (PVA) to form the composite MeO-Tpy-Zn-OAc@PVA, the material exhibits reversible writing, photochromism, and a prolonged RTP with a 14 s afterglow. These unique properties enable the composite to be utilized in potential applications such as secure data encryption and inkless printing.

X-ray/γ-ray/Ultrasound-Activated Persistent Luminescence Phosphors for Deep Tissue Bioimaging and Therapy

Persistent luminescence phosphors (PLPs) can remain luminescent after excitation ceases and have been widely explored in bioimaging and therapy since 2007. In bioimaging, PLPs can efficiently avoid tissue autofluorescence and light scattering interference by collecting persistent luminescence signals after the end of excitation. Outstanding signal-to-background ratios, high sensitivity, and resolution have been achieved in bioimaging with PLPs. In therapy, PLPs can continuously produce therapeutic molecules such as reactive oxygen species after removing excitation sources, which realizes sustained therapeutic activity after a single dose of light stimulation. However, most PLPs are activated by ultraviolet or visible light, which makes it difficult to reactivate the PLPs in vivo, particularly in deep tissues. In recent years, excitation sources with deep tissue penetration have been explored to activate PLPs, including X-ray, γ-ray, and ultrasound. Researchers found that various inorganic and organic PLPs can be activated by X-ray, γ-ray, and ultrasound, making these PLPs valuable in the imaging and therapy of deep-seated tumors. These X-ray/γ-ray/ultrasound-activated PLPs have not been systematically introduced in previous reviews. In this review, we summarize the recently developed inorganic and organic PLPs that can be activated by X-ray, γ-ray, and ultrasound to produce persistent luminescence. The biomedical applications of these PLPs in deep-tissue bioimaging and therapy are also discussed. This review can provide instructions for the design of PLPs with deep-tissue-renewable persistent luminescence and further promote the applications of PLPs in phototheranostics, noninvasive biosensing devices, and energy harvesting.

Cocrystallization-Induced Red Ultralong Organic Phosphorescence

Organic cocrystals formed through multicomponent self-assembly have attracted significant interest owing to their clear structure and tunable optical properties. However, most cocrystal systems suffer from inefficient long-wavelength emission and low phosphorescence efficiency due to strong non-radiative processes governed by the energy gap law. Herein, an efficient long-lived red afterglow is achieved using a pyrene (Py) cocrystal system incorporating a second component (NPYC4) with thermally activated delayed fluorescence (TADF) and ultralong organic phosphorescence (UOP) properties. The cocrystal (NPYC4-Py) not only inherits the excellent luminescence of its monomeric counterparts, but also exhibits unique dual-mode characteristics, including persistent TADF and UOP emission with a high quantum yield of 58 % and a lifetime of 362 ms. The precise cocrystal stacking distinctly reveals that intermolecular interactions lock the cocrystal formation and weaken the intermolecular π-π interactions between NPYC4 and Py, thereby stabilizing the excited triplet excitons. Furthermore, the favorable energy level of NPYC4 acts as a bridge, reducing the energy gap between the S1 and T1 states for Py, therefore activating its red phosphorescence from Py. This research provides direct insights into achieving efficient red UOP through co-crystallization.

Hierarchical Dual-Mode Efficient Tunable Afterglow via J-Aggregates in Single-Phosphor-Doped Polymer

The development of polymer-based persistent luminescence materials with color-tunable organic afterglow and multiple responses is highly desirable for applications in anti-counterfeiting, flexible displays, and data-storage. However, achieving efficient persistent luminescence from a single-phosphor system with multiple responses remains a challenging task. Herein, by doping 9H-pyrido[3,4-b]indole (PI2) into an amorphous polyacrylamide matrix, a hierarchical dual-mode emission system is developed, which exhibits color-tunable afterglow due to excitation-, temperature-, and humidity-dependence. Notably, the coexistence of the isolated state and J-aggregate state of the guest molecule not only provides an excitation-dependent afterglow color, but also leads to a hierarchical temperature-dependent afterglow color resulting from different thermally activated delayed fluorescence (TADF) and ultralong organic phosphorescence (UOP) behaviors of the isolated and aggregated states. The complex responsiveness based on the hierarchical dual-mode emission can serve for security features through inkjet printing and ink-writing. These findings may provide further insight into the regulated persistent luminescence by isolated and aggregated phosphors in doped polymer systems and expand the scope of stimuli-responsive organic afterglow materials for broader applications.

Achieving Near-Infrared Phosphorescence Supramolecular Hydrogel Based on Amphiphilic Bromonaphthalimide Pyridinium Hierarchical Assembly

Phosphorescent supramolecular hydrogels are currently a prevalent topic for their great promise in various photonic applications. Herein, an efficient near-infrared (NIR) phosphorescence supramolecular hydrogel is reported via the hierarchical assembly strategy in aqueous solution, which is fabricated from amphiphilic bromonaphthalimide pyridinium derivative (G), exfoliated Laponite (LP) nanosheets, and polymeric polyacrylamide (PAAm). Initially, G spontaneously self-aggregates into spherical nanoparticles covered with positively charged pyridinium units and emits single fluorescence at 410 nm. Driven by electrostatic interactions with negatively charged nanosheets, the nanoparticles subsequently function as the cross-linked binders and coassemble with LP into supramolecular hydrogels with an engendered red room-temperature phosphorescence (RTP) up to 620 nm. Benefiting from hydrogen-bonding interactions-mediated physical cross-linkage, the further introduction of PAAm not only significantly elevates the mechanical strength of the hydrogels showing fast self-healing capability, but also increases phosphorescence lifetime from 2.49 to 4.20 ms, especially generating phosphorescence at even higher temperature (τ 363 K = 2.46 ms). Additionally, efficient RTP energy transfer occurs after doping a small amount of organic dye heptamethine cyanine (IR780) as an acceptor into hydrogels, resulting in a long-lived NIR emission at 823 nm with a high donor/acceptor ratio, which is successfully applied for cell labeling in the NIR window.

Metal ion-manipulated afterglow on rhodamine 6G derivative-doped room-temperature phosphorescent PVA films

The long-lived room-temperature phosphorescence (RTP) originating from thiophene boronate polyvinyl alcohol (PVA) has enabled the creation of metal-ion-responsive RTP films doped with spirolactam ring-containing rhodamine 6G (1). In this study, RTP-active PVA films, namely, TDB@PVA and ATB@PVA, were prepared through boronate esterification of thiophene-2,5-diboronic acid (TDB) and 5-acetylthiophene-2-boronic acid (ATB) with the diol units of PVA. The delayed emission properties were evaluated, revealing an emission band at 477 nm with a turquoise afterglow for TDB@PVA and at 510 nm with a green afterglow for ATB@PVA after UV light irradiation ceased. The photophysical properties were assessed using TD-DFT and DFT calculations at the B3LYP/cc-pVDZ level. N-(rhodamine-6G)lactam dye with a salicylimine unit (1) was doped into the RTP-based PVA films, producing a multicolored afterglow upon the addition of metal ions. This phenomenon is explained by a triplet-to-singlet Förster-type resonance energy transfer process from the cross-linked thiophene boronate in PVA to the metal-ion-activated colored form of 1. This photophysical feature finds applicability in encryption techniques. Notably, the reversible metal-ligand coordination of 1 in the PVA system enabled a write/erase information process.

Utilizing weakly donor-acceptor ternary π-conjugated architecture to achieve single-component white luminescence and stimulus-responsive room-temperature phosphorescence

Purely organic room-temperature phosphorescence (RTP) has garnered substantial attention for its delayed emission, environmental sensitivity, and potential diverse applications. However, the quest for high-performance RTP materials has always been a challenge. In this study, we introduce novel weakly donor-acceptor (D-A) ternary π-conjugated architecture to construct an efficient RTP system. The strategy utilizes synergistic effects of the analogous El-Sayed rule, halogen-free heavy-atom effect, reduction of the singlet-triplet energy gap, and manipulation of flexible molecular conformation. A remarkable enhancement in the phosphorescence-to-fluorescence ratio was achieved, elevating from 0.4 in carbazole to 35.2 in DBTDBTCZ. Furthermore, the RTP system demonstrates single-component white luminescence, yielding warm and cool white colors. Intriguingly, we unveil the novel position-dependent heavy-atom effects, discerningly promoting intersystem crossing or phosphorescence decay. Benefiting from efficient RTP, multifunctional applications of real-time humidity monitoring, oxygen sensing, anti-counterfeiting labeling, and white lighting are demonstrated.

3D Printed Room Temperature Phosphorescence Materials Enabled by Edible Natural Konjac Glucomannan

Shaping room temperature phosphorescence (RTP) materials into 3D bodies is important for stereoscopic optoelectronic displays but remains challenging due to their poor processability and mechanical properties. Here, konjac glucomannan (KGM) is employed to anchor arylboronic acids with various π conjugations via a facile B─O covalent reaction to afford printable inks, using which full-color high-fidelity 3D RTP objects with high mechanical strength can be obtained via direct ink writing-based 3D printing and freeze-drying. The doubly rigid structure supplied by the synergy of hydrogen bonding and B─O covalent bonding can protect the triplet excitons; thus, the prepared 3D RTP object shows a striking lifetime of 2.14 s. The printed counterparts are successfully used for 3D anti-counterfeiting and can be recycled and reprinted nondestructively by dissolving in water. This success expands the scope of printable 3D luminescent materials, providing an eco-friendly platform for the additive manufacturing of sophisticated 3D RTP architectures.

Stepwise Stiffening Chromophore Strategy Realizes a Series of Ultralong Blue Room-Temperature Phosphorescent Materials

Ultralong room-temperature phosphorescent (URTP) materials have attracted wide attention in anti-counterfeiting, optoelectronic display, and bio-imaging due to their special optical properties. However, room-temperature blue phosphorescent materials are very scarce during applications because of the need to simultaneously populate and stabilize high-energy excited states. In this work, a stepwise stiffening chromophore strategy is proposed to suppress non-radiative jump by continuously reducing the internal spin of the chromophore, and successfully developing a series of blue phosphorescent materials. Phosphorescence lifetimes of more than 3 s are achieved, with the longest lifetime reaching 5.44 s and lasting more than 70 s in the naked eye. As far as is know, this is the best result that has been reported. By adjusting the chromophore conjugation, multicolor phosphorescences from cyan to green have been realized. In addition, these chromophores exhibit the same excellent optical properties in urea and polyvinyl alcohmance (PVA). Finally, these materials are successfully applied to luminescent displays.

Resonance-Induced Dynamic Triplet Exciton Population for Photoactivated Organic Ultralong Room Temperature Phosphorescence

Dynamically populating triplet excitons under external stimuli is desired to develop smart optoelectronic materials, but it remains a formidable challenge. Herein, we report a resonance-induced excited state regulation strategy to dynamically modulate the triplet exciton population by introducing a self-adaptive N-C═O structure to phosphors. The developed phosphors activated under high-power ultraviolet irradiation exhibited enhanced photoactivated organic ultralong room temperature phosphorescence (PA-OURTP) with lifetimes of up to ∼500 ms. The enhanced PA-OURTP was ascribed to activated N-C═O resonance variation-induced intersystem crossing to generate excess triplet excitons. The excellent PA-OURTP performance and ultralong deactivation time under ambient conditions of the developed materials could function as a reusable recorded medium for time-sensitive information encryption through optical printing. This study provides an effective approach to dynamically regulating triplet excitons and offers valuable guidance to develop high-performance PA-OURTP materials for security printing applications.

Achieving Dual Emission of Fluorescence and Phosphorescence from Anti-Kasha's Metal-Organic Halides for Information Encryption

Luminescent materials typically emit their fluorescence or phosphorescence at a specific wavelength with different excitation energies via the so-called Kasha's rule. If fluorescence or phosphorescence emission via anti-Kasha's rule could be achieved, it will hold great promise for applications in many fields. In this work, we report the synthesis and characterization of new metal-organic halide materials with dual emission of efficient room-temperature phosphorescence and fluorescence, which obey anti-Kasha's rule. Here, three emitting metal-organic halides with formula [ZnX2(bidpe)] (X = Cl for 1, X = Br for 2, X = I for 3, bidpe = 4,4'-bis(imidazol-1-yl)diphenyl ether) were prepared and their photophysical properties were investigated. The complexes exhibit dual emission of fluorescence and phosphorescence via anti-Kasha's rule, and their RTP properties of resultant products are modulated by halide substitution synthesis. DFT calculations indicate that the singlet states exhibit a halide-ligand charge transfer (XLCT) character while the triplet states are dominated by the intraligand π-π* transitions. Furthermore, the multilevel information encryption and anticounterfeiting applications are developed by virtue of anti-Kasha's rule emission.

Surface coating induced room-temperature phosphorescence in flexible organic single crystals

Materials exhibiting room temperature phosphorescence (RTP) are in high demand for signage, information encryption, sensing, and biological imaging. Due to weak spin-orbit coupling and other non-radiative processes that effectively quench the triplet excited states, RTP is sparsely observed in organic materials. Although the incorporation of a heavy atom through covalent or non-covalent modification circumvents these drawbacks, heavy-atom-containing materials are undesirable because of their deleterious side effects. Here, we designed and synthesized a new naphthalidenimine-boron complex as a coating material for the single crystals of 4,4'-dimethoxybenzophenone. The coated surface was observed to exhibit yellowish-green phosphorescence with ms lifetimes at ambient conditions through Förster resonance energy transfer (FRET). Importantly, the mechanical flexibility of the single crystals was observed to be retained after coating. The fluorescence-phosphorescence dual emission was utilised for colour-tunable optical waveguiding and anti-counterfeiting applications. As organic single crystals that can sustain mechanical deformations are emerging as the next-generation materials for electronic device fabrication, the flexible RTP organic crystals showing colour-tuneable optical waveguiding could be omnipotent in electronics.

Blue Long Afterglow and Ultra Broadband Vis-NIR Emission from All-Inorganic Copper-Doped Silver Halide Single Crystals

All-inorganic metal halides with afterglow emission have attracted increasing attention due to their significantly longer afterglow duration and higher stability compared to their organic-inorganic hybrid counterparts. However, their afterglow colors have not yet reached the blue spectral region. Here, we report all-inorganic copper-doped Rb2AgBr3 single crystals with ultralong blue afterglow (>300 s) by modulating defect states through doping engineering. The introduction of copper(I) ions into Rb2AgBr3 facilitates the formation of bromine vacancies, thus increasing the density of trap states available for charge storage and enabling bright, persistent emission after ceasing the excitation. Moreover, cascade energy transfer between distinct emissive centers in the crystals results in ultra-broadband photoluminescence, not only covering the whole white light with near-unity quantum yield but also extending into the near-infrared region. This 'cocktail' of exotic light-emission properties, in conjunction with the excellent stability of copper-doped Rb2AgBr3 crystals, allowed us to demonstrate their implementation to solid-state lighting, night vision, and intelligent anti-counterfeiting.

Modulating Heavy Atom Effect in Germylene for Persistent Room Temperature Phosphorescence

It is worth but still challenging to develop the low-valent main group compounds with persistent room temperature phosphorescence (pRTP). Herein, we presented germylene-based persistent phosphors by introduction of low-valent Ge center into chromophore. A novel phosphors CzGe and its series of derivatives, namely CzGeS, CzGeSe, CzGeAu, and CzGeCu, were synthesized. Experiments and theoretical calculations reveal that the pRTP behavior were "turn on" due to the heavy atom effect of germylene. More importantly, the low-valent of oxidation state and structural traits propelled GeCz had a balance between the intersystem crossing and the shortening of lifetime caused by the heavy atoms, resulting the ultralong lifetime of 309 ms and phosphorescent quantum efficiency of 15.84 %, which is remarkable among heavy main group phosphors. This research provides valuable insights to the design of heavy atoms in phosphors and expand the applications of germylene chemistry.

Achieving long-lived white circularly polarized luminescence from carbonized polymer dots via phosphorescence resonance energy transfer

Achieving white-light emission, especially long-lived white circularly polarized luminescence, is challenging. Herein, chiral phosphorescent carbonized polymer dots (CPDs) have been prepared by using chiral polymer sodium alginate and chiral small molecule L-lysine as precursors. Benefiting from the efficient triplet-to-singlet phosphorescence resonance energy transfer (PRET), CPD-based long-lived warm white CPL has been achieved for the first time. This study provides a universal strategy for the convenient and efficient preparation of CPD-based long-lived white CPL materials.

Tailoring raloxifene into single-component molecular crystals possessing multilevel stimuli-responsive room-temperature phosphorescence

Simultaneously achieving room-temperature phosphorescence (RTP) and multiple-stimuli responsiveness in a single-component system is of significance but remains challenging. Crystallization has been recognized to be a workable strategy to fulfill the above task. However, how the molecular packing mode affects the intersystem crossing and RTP lifetime concurrently remains unclear so far. Herein, four economic small-molecular compounds, analogues of the famous drug raloxifene (RALO), are facilely synthesized and further explored as neat single-component and stimuli-responsive RTP emitters via crystallization engineering. Thanks to their simple structures and high ease to crystallize, these raloxifene analogues function as models to clarify the important role of molecular packing in the RTP and stimuli-responsiveness properties. Thorough combination of the single-crystal structure analysis and theoretical calculations clearly manifests that the tight antiparallel molecular packing mode is the key point to their RTP behaviors. Interestingly, harnessing the controllable and reversible phase transitions of the two polymorphs of RALO-OAc driven by mechanical force, solvent vapor, and heat, a single-component multilevel stimuli-responsive platform with tunable emission color is established and further exploited for optical information encryption. This work would shed light on the rational design of multi-stimuli responsive RTP systems based on single-component organics.

Simultaneous enhancement in phosphorescence and its lifetime of PtOEP-peptide assembly triggered by protein interaction

We fabricated hybrid nanoparticles consisting of organic semiconducting material with peptide sequence to reflect the target protein interaction. A phosphorescent OLED material, platinum octaethylporphyrin (PtOEP) was self-assembled by reprecipitation with the A17 peptide (YCAYYSPRHKTTF) selected as a probe ligand in order to recognize heat shock protein 70 (HSP70). The phosphorescence intensity of the PtOEP-A17 assembly was enhanced by 125 % after treatment with HSP70. The specificity of the protein interaction was confirmed in both solution and solid states of the PtOEP-A17 assembly against to BSA and nucleolin. We figured out that the phosphorescence lifetime of PtOEP-A17 assembly after exposed to HSP70 increased significantly to 153 ns from initial 115 ns. These simultaneous enhancements in phosphorescence and lifetime triggered by the specific protein interaction would open new applications of PtOEP, a representative material of light-emitting device fields.

The Role of Aqueous Solvation on the Intersystem Crossing of Nitrophenols

The photochemistry of nitrophenols is a source of smog as nitrous acid is formed from their photolysis. Nevertheless, computational studies of the photochemistry of these widespread toxic molecules are scarce. In this work, the initial photodeactivation of ortho-nitrophenol and para-nitrophenol is modeled, both in gas phase and in aqueous solution to simulate atmospheric and aerosol environments. A large number of excited states, six for ortho-nitrophenol and 11 for para-nitrophenol, have been included and were all populated during the decay. Moreover, periodic time-dependent density functional theory (TDDFT) is used for both the explicitly included solvent and the solute. A comparison to periodic QM/MM (TDDFT/MM), with electrostatic embedding, is made, showing notable differences between the decays of solvated nitrophenols simulated with QM/MM and full (TD)DFT. A reduced intersystem crossing in aqueous solution could be observed thanks to the surface hopping approach using explicit, periodic TDDFT solvation including spin-orbit couplings.

Rapid room-temperature phosphorescence chiral recognition of natural amino acids

Chiral recognition of amino acids is very important in both chemical and life sciences. Although chiral recognition with luminescence has many advantages such as being inexpensive, it is usually slow and lacks generality as the recognition module relies on structural complementarity. Here, we show that one single molecular-solid sensor, L-phenylalanine derived benzamide, can manifest the structural difference between the natural, left-handed amino acid and its right-handed counterpart via the difference of room-temperature phosphorescence (RTP) irrespective of the specific chemical structure. To realize rapid and reliable sensing, the doped samples are obtained as nanocrystals from evaporation of the tetrahydrofuran solutions, which allows for efficient triplet-triplet energy transfer to the chiral analytes generated in situ from chiral amino acids. The results show that L-analytes induce strong RTP, whereas the unnatural D-analytes produce barely any afterglow. The method expands the scope of luminescence chiral sensing by lessening the requirement for specific molecular structures.

Phosphorescent acyclic cucurbituril solid supramolecular multicolour delayed fluorescence behaviour

Organic photoluminescent macrocyclic hosts have been widely advanced in many fields. Phosphorescent hosts with the ability to bind organic guests have rarely been reported. Herein, acyclic cucurbituril modified with four carboxylic acids (ACB-COOH) is mined to present uncommon purely organic room-temperature phosphorescence (RTP) at 510 nm with a lifetime of 1.86 μs. Its RTP properties are significantly promoted with an extended lifetime up to 2.12 s and considerable quantum yield of 6.29% after assembly with a polyvinyl alcohol (PVA) matrix. By virtue of the intrinsic self-crimping configuration of ACB-COOH, organic guests, including fluorescence dyes (Rhodamine B (RhB) and Pyronin Y (PyY)) and a drug molecule (morphine (Mor)), could be fully encapsulated by ACB-COOH to attain energy transfer involving phosphorescent acyclic cucurbituril. Ultimately, as-prepared systems are successfully exploited to establish multicolor afterglow materials and visible sensing of morphine. As an expansion of phosphorescent acyclic cucurbituril, the host afterglow color can be readily regulated by attaching different aromatic sidewalls. This study develops the fabrication strategies and application scope of a supramolecular phosphorescent host and opens up a new direction for the manufacture of intelligent long-lived luminescent materials.

Sunlight-Activated Hour-Long Afterglow from Transparent and Flexible Polymers

Afterglow materials featuring long emission durations ranging from milliseconds to hours have garnered increasing interest owing to their potential applications in sensing, bioimaging, and anti-counterfeiting. Unfortunately, polymeric materials rarely exhibit afterglow properties under ambient conditions because of the rapid nonradiative decay rate of triplet excitons. In this study, hour-long afterglow (HLA) polymer films are fabricated using a facile molecular doping strategy. Flexible and transparent polymer films emitted a bright afterglow lasting over 11 h at room temperature in air, which is one of the best performances among the organic afterglow materials reported to date. Intriguingly, HLA polymer films can be activated by sunlight, and their cyan afterglow in air can be readily observed by the naked eye. Moreover, the HLA color of the polymer films could be tuned from cyan to red through the Förster resonance energy transfer mechanism. Their application in flexible displays and information storage has also been demonstrated. With remarkable advantages, including an hour-long and bright afterglow, tunable afterglow colors, superior flexibility and transparency, and ease of fabrication, the HLA polymer paves the way for the practical application of afterglow materials in the engineering sector.

Printable Block Molecular Assemblies with Controlled Exciton Dynamics

Creating hierarchical molecular block heterostructures, with the control over size, shape, optical, and electronic properties of each nanostructured building block can help develop functional applications, such as information storage, nanowire spectrometry, and photonic computing. However, achieving precise control over the position of molecular assemblies, and the dynamics of excitons in each block, remains a challenge. In the present work, the first fabrication of molecular heterostructures with the control of exciton dynamics in each block, is demonstrated. Additionally, these heterostructures are printable and can be precisely positioned using Direct Ink Writing-based (DIW) 3D printing technique, resulting in programable patterns. Singlet excitons with emission lifetimes on nanosecond or microsecond timescales and triplet excitons with emission lifetimes on millisecond timescales appear simultaneously in different building blocks, with an efficient energy transfer process in the heterojunction. These organic materials also exhibit stimuli-responsive emission by changing the power or wavelength of the excitation laser. Potential applications of these organic heterostructures in integrated photonics, where the versatility of fluorescence, phosphorescence, efficient energy transfer, printability, and stimulus sensitivity co-exist in a single nanowire, are foreseen.

Recent progress in ion-regulated organic room-temperature phosphorescence

Organic room-temperature phosphorescence (RTP) materials have attracted considerable attention for their extended afterglow at ambient conditions, eco-friendliness, and wide-ranging applications in bio-imaging, data storage, security inks, and emergency illumination. Significant advancements have been achieved in recent years in developing highly efficient RTP materials by manipulating the intermolecular interactions. In this perspective, we have summarized recent advances in ion-regulated organic RTP materials based on the roles and interactions of ions, including the ion-π interactions, electrostatic interactions, and coordinate interactions. Subsequently, the current challenges and prospects of utilizing ionic interactions for inducing and modulating the phosphorescent properties are presented. It is anticipated that this perspective will provide basic guidelines for fabricating novel ionic RTP materials and further extend their application potential.

Ground-State Orbital Descriptors for Accelerated Development of Organic Room-Temperature Phosphorescent Materials

Organic materials with room-temperature phosphorescence (RTP) are in high demand for optoelectronics and bioelectronics. Developing RTP materials highly relies on expert experience and costly excited-state calculations. It is a challenge to find a tool for effectively screening RTP materials. Herein we first establish ground-state orbital descriptors (πFMOs ) derived from the π-electron component of the frontier molecular orbitals to characterize the RTP lifetime (τp ), achieving a balance in screening efficiency and accuracy. Using the πFMOs , a data-driven machine learning model gains a high accuracy in classifying long τp , filtering out 836 candidates with long-lived RTP from a virtual library of 19,295 molecules. With the aid of the excited-state calculations, 287 compounds are predicted with high RTP efficiency. Impressively, experiments further confirm the reliability of this workflow, opening a novel avenue for designing high-performance RTP materials for potential applications.

Enabling Highly Robust Full-Color Ultralong Room-Temperature Phosphorescence and Stable White Organic Afterglow from Polycyclic Aromatic Hydrocarbons

In this work, full-color and stable white organic afterglow materials with outstanding water, organic solvents, and temperature resistances have been developed for the first time by embedding the selected polycyclic aromatic hydrocarbons into melamine-formaldehyde polymer via solution polymerization. The afterglow quantum yields and lifetimes of the resulting polymer films were up to 22.7 % and 4.83 s, respectively, under ambient conditions. For the coronene-doped sample, its afterglow color could be linearly tuned between yellow and blue by adjusting the temperature, and it could still emit an intense blue afterglow with a lifetime of 0.68 s at 440 K. Moreover, the films showed a bright and stable white afterglow at 370 K with a lifetime of 2.80 s and maintained an excellent afterglow performance after soaking in water and organic solvents for more than 150 days. In addition, the application potential of the polymer films in information encryption and anti-counterfeiting was also demonstrated.

Side group dependent room temperature crystallization-induced phosphorescence of benzil based all organic phosphors

In this work, we report alkoxy substituted benzil based all organic room temperature phosphors which showed crystallization induced phosphorescence (CIP). Nine title compounds were prepared with various alkyl lengths (OCnH2n+1: n = 8-16) and the effect of alkyl side group length on the phosphorescence performance was investigated, as compared to p-anisil. It was found that both phosphorescence quantum yield and lifetime increased concomitantly as the alkyl length increased up to nonyloxy (BZL-OC9). Further increase in the carbon number caused the phosphorescence performance to deteriorate due to greater conformational freedom of the side groups. An incredible quantum yield of 70% was achieved for BZL-OC9. A promising finding is that the increased quantum yield was accompanied by the increase in the lifetime relative to p-anisil, which has been historically challenging. Single crystallography coupled with UV-Vis spectroscopy revealed that a higher level of intermolecular π-π interactions was observed from p-anisil while more alkyl interactions with less intermolecular π-orbital overlap were found for BZL-OC8. As a result, molecular rigidification with less phosphorescence quenching was achieved for BZL-OC8 leading to enhanced performance. A precipitation study on a dichloromethane solution as a function of the content of MeOH (poor solvent) proved that the emission of the BZL-OCn system is truly aggregation-induced. The current work demonstrates that strategic side group engineering could be a promising approach to developing high-performance all organic phosphors as well as improving the properties of existing phosphors.

Thia[n]helicenes with long persistent phosphorescence

Helicenes with persistent luminescence have received relatively little attention, despite their demonstrated highly efficient intersystem crossing (ISC) from the excited singlet to the triplet state. Herein, we designed a series of ortho-fused aromatics by combining dithieno[2,3-b:3',2'-d]thiophene (DTT) with annulated benzene fragments, denoted as TB[n]H (n = 3-8), to achieve persistent luminescence. Wherein, thia[n]helicenes (n = 5-8) exhibited intense phosphorescence with millisecond-range lifetimes (τp) at 77 K. Particularly interesting was the observation that the odd-numbered ring helicenes displayed longer τp values than their neighboring even-numbered counterparts. Notably, TB[7]H showcased the longest τp of 628 ms. This phenomenon can be attributed to the more favorable ISC channels and stronger spin-orbital coupling (SOC) of old-numbered helicenes than even-numbered ones. Furthermore, both conformers of TB[7]H exhibited significant circularly polarized phosphorescent (CPP) responses, with luminescence dissymmetry factors (glum) of 0.015 and -0.014. These discoveries suggest that thiahelicenes may be a specific class of organic phosphorescent and CPP materials.

Enabling Carbonized Polymer Dots with Color-tunable Time-dependent Room Temperature Phosphorescence through Confining Carboxyl Dimer Association

Developing a facile strategy to realize fine-tuning of phosphorescence color in time-dependent room temperature phosphorescence (RTP) materials is essential but both theoretically and practically rarely exploited. Through simultaneously confining carboxyl dimer association and isolated carboxyl into the particle via a simple hydrothermal treatment of polyacrylic acid, a dual-peak emission of red phosphorescence (645 nm) and green phosphorescence (550 nm) was observed from carbonized polymer dots (CPDs). The ratio of the two luminescent species can be well regulated by hydrochloric acid inhibiting the dissociation of carboxyl to promote hydrogen bond. Due to comparable but different lifetimes, color-tunable time-dependent RTP with color changing from yellow to green or orange to green were obtained. Based on the crosslinking enhanced emission effect, the phosphorescence visible time was even extended to 7 s through introducing polyethylenimide. This study not only proposes a novel and facile method for developing CPDs with color-tunable time-dependent RTP, but also provides a bran-new non-conjugated red phosphorescence unit and its definite structure.

Molecularly Engineered Room-Temperature Phosphorescence for Biomedical Application: From the Visible toward Second Near-Infrared Window

Phosphorescence, characterized by luminescent lifetimes significantly longer than that of biological autofluorescence under ambient environment, is of great value for biomedical applications. Academic evidence of fluorescence imaging indicates that virtually all imaging metrics (sensitivity, resolution, and penetration depths) are improved when progressing into longer wavelength regions, especially the recently reported second near-infrared (NIR-II, 1000-1700 nm) window. Although the emission wavelength of probes does matter, it is not clear whether the guideline of "the longer the wavelength, the better the imaging effect" is still suitable for developing phosphorescent probes. For tissue-specific bioimaging, long-lived probes, even if they emit visible phosphorescence, enable accurate visualization of large deep tissues. For studies dealing with bioimaging of tiny biological architectures or dynamic physiopathological activities, the prerequisite is rigorous planning of long-wavelength phosphorescence, being aware of the cooperative contribution of long wavelengths and long lifetimes for improving the spatiotemporal resolution, penetration depth, and sensitivity of bioimaging. In this Review, emerging molecular engineering methods of room-temperature phosphorescence are discussed through the lens of photophysical mechanisms. We highlight the roles of phosphorescence with emission from visible to NIR-II windows toward bioapplications. To appreciate such advances, challenges and prospects in rapidly growing studies of room-temperature phosphorescence are described.

Microwave-Responsive Flexible Room-Temperature Phosphorescence Materials Based on Poly(vinylidene fluoride) Polymer

The development of flexible, room-temperature phosphorescence (RTP) materials remains challenging owing to the quenching of their unstable triplet excitons via molecular motion. Therefore, a polymer matrix with Tg higher than room temperature is required to prevent polymer segment movement. In this study, a RTP material was developed by incorporating a 4-biphenylboronic acid (BPBA) phosphor into a poly(vinylidene fluoride) (PVDF) matrix (Tg =-27.1 °C), which exhibits a remarkable UV-light-dependent oxygen consumption phosphorescence with a lifetime of 1275.7 ms. The adjustable RTP performance is influenced by the crystallinity and polymorph (α, β, and γ phases) fraction of PVDF, therefore, the low Tg of the PVDF matrix enables the polymeric segmental motion upon microwave irradiation. Consequently, a reduction in the crystallinity and an increase in the α phase fraction in PVDF film induces RTP after 2.45 GHz microwave irradiation. These findings open up new avenues for constructing crystalline and phase-dependent RTP materials while demonstrating a promising approach toward microwave detection.

Phosphorescence resonance energy transfer from purely organic supramolecular assembly

Phosphorescence energy transfer systems have been applied in encryption, biomedical imaging and chemical sensing. These systems exhibit ultra-large Stokes shifts, high quantum yields and are colour-tuneable with long-wavelength afterglow fluorescence (particularly in the near-infrared) under ambient conditions. This review discusses triplet-to-singlet PRET or triplet-to-singlet-to-singlet cascaded PRET systems based on macrocyclic or assembly-confined purely organic phosphorescence introducing the critical toles of supramolecular noncovalent interactions in the process. These interactions promote intersystem crossing, restricting the motion of phosphors, minimizing non-radiative decay and organizing donor-acceptor pairs in close proximity. We discuss the applications of these systems and focus on the challenges ahead in facilitating their further development.

Evolution of organic phosphor through precision regulation of nonradiative decay

Development of single-component organic phosphor attracts increasing interest due to its wide applications in optoelectronic technologies. Theoretically, activating efficient intersystem crossing (ISC) via 1(π, π*) to 3(π, π*) transitions, rather than 1(n, π*) → 3(π, π*) transitions, is an alternative access to purely organic phosphors but remains challenging. Herein, we designed and successfully synthesized the sila-8-membered ring fused biaryl benzoskeleton by transition metal catalysis, which served as a new organic phosphor with efficient 1(π, π*) to 3(π, π*) ISC. We first found that such a compound exhibits a record-long phosphorescence lifetime of 6.5 s at low temperature for single-component organic systems. Then, we developed two strategies to tune their decay channels to evolve such nonemissive molecules into bright phosphors with elongated lifetimes at room temperature: 1) Physic-based design, where quantitative analyses of electron-phonon coupling led us to reveal and hinder the major nonradiative channels, thus lighted up room temperature phosphorescence (RTP) with a lifetime of 480 ms at 298 K; 2) chemical geometry-driven molecular engineering, where a geometry-based descriptor ΔΘT1-S0/ΘS0 was developed for rational screening RTP candidates and further improved the RTP lifetime to 794 ms. This study clearly shows the power of interdiscipline among synthetic methodology, physics-based rational design, and computational modeling, which represents a paradigm for the development of an organic emitter.

Tunable Afterglow and Self-Trapped Exciton Emissions in Zr (IV)-Based Organic-Inorganic Metal Halide Hybrids by Metal-Ion Doping

Low-dimensional hybrid metal halide (LDHMH) materials have attracted considerable attention owing to their intriguing optical properties. To the best of the knowledge, this is the first study to successfully demonstrate both self-trap exciton (STE) and afterglow emissions in Zr-based LDHMH materials. The obtained pure (Ph3 S)2 ZrCl6 crystals showed near-ultraviolet phosphorescence and a green afterglow owing to the organic cation Ph3 S+ , while the Bi-doped and Sb-doped crystals exhibited both STE and afterglow emissions. However, the Te-doped crystals showed only a broad yellow STE emission owing to the [TeCl6 ]2- octahedron. In addition, all the crystals showed good stability. Notably, Sb-doped crystals produced white light, which can be adjusted between cold white and warm white using different excitations. Finally, this strategy for both STE and afterglow emissions can be applied to other LDHMH materials for optical applications.

Theoretical exploration of the bromine substitution effect and hydrostatic pressure responsive mechanism for room temperature phosphorescence

Stimulus-responsive organic room temperature phosphorescence (RTP) materials with long lifetimes, high efficiencies and tunable emission properties have broad applications. However, the amounts and species of efficient RTP materials are far from meeting the requirements and the inner stimulus-responsive mechanisms are unclear. Therefore, developing efficient stimulus-responsive RTP materials is highly desired and the relationship between the molecular structures and luminescent properties of RTP materials needs to be clarified. Based on this point, the influences of different substitution sites of Br on the luminescent properties of RTP molecules are studied by the combined quantum mechanics and molecular mechanics (QM/MM) coupled with thermal vibration correlation function (TVCF) theory. Moreover, the hydrostatic pressure effect on the efficiencies and lifetimes is explored and the inner mechanism is illustrated. The results show that, for the exciton conversion process, the o-substitution molecule possesses the largest spin-orbit coupling (SOC) value (〈S1|Ĥso|T1〉) in the intersystem crossing (ISC) process and this is conducive to the accumulation of triplet excitons. However, for the energy consumption process, the large SOC value (〈S0|Ĥso|T1〉) for the p-substitution molecule brings a fast non-radiative decay rate, and the small SOC value for the m-substitution molecule generates a decreased non-radiative decay rate which is helpful for realizing long lifetime emission. Keeping with this perspective, the conflict between high exciton utilization and long RTP emission needs to be balanced rather than enhancing the SOC effect by simply adding heavy atoms in RTP systems. Through regulating the molecular stacking modes by the hydrostatic pressure effect, the inner stimulus-responsive mechanism is revealed. The data of 〈S1|Ĥso|T1〉 in the ISC process remain almost unchanged, while 〈S0|Ĥso|T1〉 values and transition dipole moments are sensitive to the hydrostatic pressure. Under 1 GPa, the RTP molecule achieves a maximum efficiency (81.17%) and long lifetime (2.72 ms) with the smallest SOC and decreased non-radiative decay rate. To our knowledge, this is the first time that the hydrostatic pressure responsive mechanism for RTP molecules is revealed from a theoretical perspective, and the relationships between molecular structures and luminescent properties are detected. Our work could facilitate the development of high performance RTP molecules and expand their applications in multilevel information encryption.

Achieving Stable and Switchable Ultralong Room-Temperature Phosphorescence from Polymer-Based Luminescent Materials with Three-Dimensional Covalent Networks for Light-Manipulated Anticounterfeiting

Developing polymer-based organic afterglow materials with switchable ultralong organic phosphorescence (UOP) that are insensitive to moisture remains challenging. Herein, two organic luminogens, BBCC and BBCS, were synthesized by attaching 7H-benzo[c]carbazole (BBC) to benzophenone and diphenyl sulfone. These two emitters were employed as guest molecules and doped into epoxy polymers (EPs), which were constructed by in situ polymerization to achieve polymer materials BBCC-EP and BBCS-EP. It was found that BBCC-EP and BBCS-EP films exhibited significant photoactivated UOP properties. After light irradiation, they could produce a conspicuous organic afterglow with phosphorescence quantum yields and lifetimes up to 5.35% and 1.91 s, respectively. Meanwhile, BBCS-EP also presented photochromic characteristics. Upon thermal annealing, the UOP could be turned off, and the polymer films recovered to their pristine state, showing switchable organic afterglow. In addition, BBCC-EP and BBCS-EP displayed excellent water resistance and still produced obvious UOP after soaking in water for 4 weeks. Inspired by the unique photoactivated UOP and photochromic properties, BBCC and BBCS in the mixtures of diglycidyl ether of bisphenol A (DGEBA) and 1,3-propanediamine were employed as security inks for light-controlled multilevel anticounterfeiting. This work may provide helpful guidance for developing photostimuli-responsive polymer-based organic afterglow materials, especially those with stable UOP under ambient conditions.

Room temperature phosphorescence from natural wood activated by external chloride anion treatment

Producing afterglow room temperature phosphorescence (RTP) from natural sources is an attractive approach to sustainable RTP materials. However, converting natural resources to RTP materials often requires toxic reagents or complex processing. Here we report that natural wood may be converted into a viable RTP material by treating with magnesium chloride. Specifically, immersing natural wood into an aqueous MgCl₂ solution at room temperature produces so-called C-wood containing chloride anions that act to promote spin orbit coupling (SOC) and increase the RTP lifetime. Produced in this manner, C-wood exhibits an intense RTP emission with a lifetime of ~ 297 ms (vs. the ca. 17.5 ms seen for natural wood). As a demonstration of potential utility, an afterglow wood sculpture is prepared in situ by simply spraying the original sculpture with a MgCl₂ solution. C-wood was also mixed with polypropylene (PP) to generate printable afterglow fibers suitable for the fabrication of luminescent plastics via 3D printing. We anticipate that the present study will facilitate the development of sustainable RTP materials.

Stimulus-Responsive Organic Phosphorescence Materials Based on Small Molecular Host-Guest Doped Systems

Small molecular host-guest doped materials exhibit superiority toward high-efficiency room-temperature phosphorescence (RTP) materials due to their structural design diversity and ease of preparation. Dynamic RTP materials display excellent characteristics, such as good reversibility, quick response, and tunable luminescence ability, making them applicable to various cutting-edge technologies. Herein, we summarize the advances in host-guest doped dynamic RTP materials that respond to external and internal stimuli and present some insights into the molecular design strategies and underlying mechanisms. Subsequently, specific viewpoints are described regarding this promising field for the development of dynamic RTP materials. This Perspective is highly beneficial for future intelligent applications of dynamic RTP systems.